1. Field of the Invention
The present invention relates to a method for driving an electro-optical device such as a liquid crystal display device, a driving circuit for driving an electro-optical device, an electro-optical device, and an electronic apparatus.
2. Description of Related Art
Related Art
A first background art associated with a method for driving a liquid crystal display device (based on a multi-line selection) is disclosed in International Application published as WO93/18501. In this method for driving a liquid crystal display device, a liquid crystal display panel includes scanning electrodes and signal electrodes arranged in a matrix such that the scanning electrodes and signal electrodes intersect each other, and pixels are formed in a matrix at intersections thereof. The scanning electrodes are organized into groups, each group consisting of a particular number of scanning electrodes which are selected at the same time, and the scanning electrodes are sequentially selected on a group-by-group basis. FIG. 6 illustrates an example of a set of waveforms for the case where four lines of scanning electrodes (four scanning electrodes) are selected at a time according to this driving method. In FIG. 6, Y1 to Y8 denote the waveforms of scanning voltages applied to the scanning electrodes, and X1 denotes the waveform of a signal voltage applied to a signal electrode. A selection voltage V3 or xe2x88x92V3 is applied to the scanning electrodes for a selection period (H) of each of four fields 1f-4f of one frame (F).
In this driving method, when there are a relatively large number of scanning electrodes, a liquid crystal of type 2 indicated in root-means-square voltage luminance characteristic of liquid crystal shown in FIG. 4 having a small value in terms of (saturation voltage)/(threshold voltage)=(Vs2/Vt2) is employed although a large driving voltage is required. In the case where there are a small number of scanning electrodes (for example when there are no more than about 32 scanning electrodes), a liquid crystal of type 1 having a low threshold voltage and having a large value in terms of (saturation voltage)/(threshold voltage)=(Vs1/Vt1) is employed so that the liquid crystal can be driven by a low voltage.
The operation of driving a liquid crystal of type 2 in accordance with the conventional method shown in FIG. 6 is discussed below. Herein, the liquid crystal is assumed to be driven by voltages which give a maximum value in terms of the ratio of the root-means-square value of on-voltage to the root-means-square value of off-voltage. More specifically, if a liquid crystal of type 2 with a threshold voltage Vt2 of 2.2 V is used and if the liquid crystal panel includes 64 lines of scanning electrodes, then V3 is set to about 6.7 V, and V2 to about 3.35 V. In the case where there are 120 scanning lines to be driven, V3 is set to about 8.9 V, and V2 to about 3.26 V. In any case, seven levels of driving voltages are required. Besides, the scanning electrode driving circuit is needed to output a high selection voltage. Thus, the difference between the selection voltage output from the scanning electrode driving circuit and the signal voltage output from the signal electrode driving circuit becomes great.
As a result, the conventional driving method requires a complicated power supply circuit and consumes a large amount of electric power. Furthermore, it is difficult to form both the scanning electrode driving circuit and the signal electrode driving circuit on a single IC chip. Referring to FIG. 14, a conventional power supply circuit is described below.
In this power supply circuit, a single input voltage Vcc relative to a ground voltage GND is input. A latch pulse LP is also input to the power supply circuit. Using Vcc and GND as power supply and in response to the latch pulse LP, a clock generator 21 generates a plurality of clock signals with different timing used by charge pump circuits. A negative sixfold boosting circuit 22 multiplies GND with respect to Vcc by 6 in a negative direction by means of charge pumping, thereby generating a voltage VEE. When Vcc=3.3 V, VEE becomes xe2x88x9216.5 V. In accordance with VEE, a contrast adjacent circuit 23 generates a selection voltage xe2x88x92V3 which gives optimum contrast. This selection voltage xe2x88x92V3 serves as a negative selection voltage applied to the scanning electrodes. A twofold boosting circuit 24 multiplies GND with respect to the selection voltage xe2x88x92V3 by 2 by means of charge pumping thereby generating a positive selection voltage V3. A negative twofold boosting circuit 25 multiplies GND with respect to Vcc by 2 in the negative direction by means of charge pumping thereby generating a voltage xe2x88x92V2. xc2xd dropping circuits 26 and 27 generate V1 by equally dividing between voltages Vcc and GND, and also generate xe2x88x92V1 by equally dividing between voltages GND and (xe2x88x92V2), by a charge pumping operation. GND is directly employed as a center voltage VC. A voltage V2 which is symmetric to xe2x88x92V2 about GND is generated by directly employing Vcc. Thus, all voltages required to drive the liquid crystal panel are obtained. In this power supply circuit, output voltages V3, V2, V1, VC, xe2x88x92V1, xe2x88x92V2, xe2x88x92V3 are symmetric about GND. A circuit 28 generates a voltage which is higher than xe2x88x92V3 by Vcc and supplies the resultant voltage as a logic voltage xe2x88x92VDDy to the scanning electrode driving circuit.
In the conventional technique, seven levels of driving voltages used to drive the liquid crystal display device are generated in the above-described manner using the power supply circuit. However, as described above, the power supply circuit needs a very complicated circuit configuration.
The liquid crystal of type 1 shown in FIG. 4 with a smaller threshold voltage is also used because this type of liquid crystal can be driven with a smaller voltage and thus consumes lower power. However, although liquid crystal display devices with such a liquid crystal having a low threshold voltage can be driven by a low voltage, the ratio of the root-means-square value of on-voltage to the root-means-square value of off-voltage applied to the liquid crystal is large, and thus, it is difficult to deal with a large number of scanning lines. If an attempt to drive a large number of scanning electrodes is made, degradation in contrast and irregularity results. Therefore, the upper practical limit of the number of scanning lines which can be driven is about 16 to 32.
In the conventional optimized amplitude selective addressing method, each scanning electrode is selected once during each frame period. In contrast, in the driving method in which a plurality of lines are selected at a time, selection periods are equally distributed in terms of time over each frame, while retaining normal orthogonality in the selection of scanning lines. Furthermore, in this method, scanning electrodes are selected in such a manner that a particular group (block) including a predetermined number of scanning electrodes is selected at a time, so that selected scanning electrodes are spatially distributed. Herein, the term xe2x80x9cnormalxe2x80x9d means that all scanning voltages have an equal root-means-square value amplitude) during each frame period.
The term xe2x80x9corthogonalxe2x80x9d means that when the amplitude of a voltage applied to a particular scanning electrode is multiplied by and added to the amplitude of a voltage applied to another arbitrary scanning electrode for respective selection periods over one frame period, the sum of the voltage amplitudes becomes 0. In simple matrix liquid crystal display devices, normal orthogonality is an essential prerequisite to the operation of turning each pixel on and off, independently of each other.
(Second Related Art)
A second background technique in the art of electro-optical devices such as a liquid crystal device is disposing a driving circuit in a single-chip form on either a substrate on which scanning electrodes (also called scanning lines or common electrodes) are arranged or a substrate on which signal electrodes (also called segment electrodes or data lines) are arranged, to drive these scanning electrodes and signal electrodes. In this technique, in order to connect all scanning electrode""s and all signal electrodes to the output terminals of the single-chip type driving circuit, it is required that a large number of interconnection lines be disposed in a frame region surrounding an image display region on the substrate on which the driving circuit is mounted, wherein one end of each interconnection line is connected to a corresponding output terminal of the driving circuit. The scanning electrodes or the signal electrodes disposed on the other substrate are electrically connected to the opposite ends (up-to-down conducting terminals) of particular interconnection lines via up-to-down conducting members. The employment of the single-chip type driving circuit makes it possible to realize a small-sized low-cost electro-optical device which can be advantageously employed as, for example, a small-sized liquid crystal device for use in, for example, a portable telephone.
Japanese Unexamined Patent Publication No. 60-68371 discloses an electro-optical device such as a liquid crystal display device in which signal electrodes are arranged in a multiple-fold matrix on one substrate and scanning electrodes are arranged in the form of stripes on the other substrate. In this technique, if signal electrodes are disposed in an n-fold matrix (wherein n is an integer equal to or greater than 2), it becomes possible to increase the period during which a selection voltage is applied to each pixel by a factor of n compared to that employed in the common matrix scheme, and thus, it becomes possible to form an image with higher brightness and higher contrast ratio. The multiple-fold matrix structure may also be employed not for the data lines but for the scanning lines, as disclosed for example in Japanese Unexamined Patent Publication No. 58-143373.
In electro-optical devices of the above-described types, it is generally desirable that the size of the screen relative to the total device size be as large as possible. To meet this requirement, it is desirable that the image display region in which an image is displayed be formed on the substrate such that it becomes as large as possible relative to the frame region which surrounds the image display region and in which no image is displayed.
However, when the single-chip type driving circuit is employed, it is required that a great number of interconnection lines be disposed on the substrate in the frame region such that one end of each interconnection line is connected to the single-chip type driving circuit, and thus the frame region has a large area. The area of the frame region can be reduced by reducing the width of the interconnection lines. However, this result in an increase in the resistance of the interconnection lines and thus degradation occurs in image quality. Furthermore, it becomes required that the driving circuit have a higher voltage supplying capability.
In particular, when a single-chip type driving circuit is employed in a device in which scanning electrodes are disposed on one of two substrates and signal electrodes are disposed on the other substrates, it is required that the scanning electrodes or signal electrodes disposed on the substrate opposite to the substrate on which the driving circuit is formed be connected via up-to-down conducting members to the corresponding interconnection lines formed on the substrate on which the driving circuit is formed. To meet the above requirement, up-to-down conducting terminals must be formed in the frame region wherein each up-to-down conducting member occupies a certain area including a margin for an alignment error which can occur when two substrates are bonded to each other. This also makes it further difficult to reduce the area of the frame region.
If the pixel pitch is reduced (that is, the scanning electrode pitch and the signal electrode pitch are reduced) to meet the fundamental requirement for a higher-quality display image, it will be required to increase the number of interconnection lines. This makes it further difficult to reduce the area of the frame region in which the interconnection lines are disposed. Furthermore, the problems with the high interconnection resistance and the poor voltage supplying capability of the driving circuit become more serious.
Furthermore, in electro-optical devices employing the multiple-fold matrix technique described above, interconnection lines (scanning electrodes or signal electrodes) which are arranged in a multiple-fold matrix are formed essentially in a complex manner in the image display region. Therefore, it becomes very difficult to produce such an electro-optical device in particular when a small pixel pitch is required. With the reduction in the pixel pitch, the opening area (through which light passes to form an image) of each pixel becomes extremely narrow as a result of the reduction in distance between adjacent interconnections. Thus, it is thought that the reduction in the scanning electrode pitch or the signal electrode pitch (namely, the reduction in the pixel pitch) is impractical.
It is a general object of the present invention to solve the above problems. More specifically, it is an object of the present invention to provide a method for driving an electro-optical device, a driving circuit for driving an electro-optical device, an electro-optical device, and an electronic apparatus, using a reduced number of driving voltage levels thereby making it possible to form a high-quality image display with reduced electric power consumption. It is another object of the present invention to provide an electro-optical device having a structure which makes it possible to reduce the area of a frame region relative to the area of an image display region and which also makes it possible to rather easily reduce the pixel pitch.
According to an aspect of the present invention, to solve the problems with the background arts described above, a method of driving an electro-optical device is provided including a plurality of scanning electrodes and a plurality of signal electrodes, the plurality of scanning electrodes and the plurality of signal electrodes being arranged such that they intersect each other, the plurality of scanning electrodes being organized into groups, each group consisting of a plural number of scanning electrodes which are simultaneously selected, selection of scanning electrodes being sequentially performed on a group-by-group basis, wherein the amplitude of a voltage applied to the scanning electrodes is equal to the amplitude of a voltage applied to the signal electrodes.
This driving method allows a reduction in the driving voltage and also a reduction in the number of levels associated with the driving voltage. As a result, it becomes possible to reduce the total electric power consumed by a power supply circuit which generates the driving voltage, driving circuits, the liquid crystal panel, and the like. Furthermore, the power supply circuit and the driving circuits can be constructed in simpler fashions. Still furthermore, the scanning electrode driving circuit is allowed to have a smaller breakdown voltage. This allows a reduction in cost. Still furthermore, it becomes possible to combine the power supply circuit, the control circuit, the signal electrode driving circuit, the scanning electrode driving circuit, and the like, in an integral fashion on a single chip, which results in a reduction in the total size.
In a preferable mode in the above-described method of driving an electro-optical device, scanning voltages applied to the scanning electrodes include a non-selection voltage, a first selection voltage which is positive with respect to the non-selection voltage, and a second selection voltage which is negative with respect to the non-selection voltage, wherein maximum and minimum signal voltages applied to the signal electrodes are set to be equal to the first and second selection voltages described above. This makes it possible to use the maximum and minimum driving voltages in common for both the scanning electrode driving circuit and the signal electrode driving circuit, thereby reducing the number of levels associated with the driving voltages. Furthermore, because the amplitude of the voltage is equal for both driving circuits, the driving circuits are allowed to have an equal breakdown voltage, and thus, it becomes possible to integrate both driving circuits on a single chip.
In the above-described method of driving an electro-optical device, the electro-optical device may be a liquid crystal display device, wherein it is preferable to employ a liquid crystal having a characteristic satisfying the condition: (root-means-square value of on-voltage applied to the liquid crystal)/(root-means-square value of off-voltage applied to the liquid crystal)xe2x89xa7(saturation voltage of the liquid crystal)/(threshold voltage of the liquid crystal), as a liquid crystal of the liquid crystal display device. This makes it possible to achieve high contrast using reduced driving voltages.
In the above-described method of driving an electro-optical device, the power supply circuit for generating the scanning voltages and the signal voltages preferably includes a voltage boosting circuit for generating the first selection voltage by boosting the non-selection voltage and the second selection voltage, a first voltage dropping circuit for generating the signal voltage having a voltage level between the second selection voltage and the non-selection voltage, and a second voltage dropping circuit for generating the signal voltage having a voltage level between the non-selection voltage and the second selection voltage. This allows simplification in terms of the circuit configuration of the power supply circuit compared with the conventional power supply circuit. Furthermore, it becomes possible to integrate the power supply circuit together with the driving circuits on a single-chip integrated circuit.
In the above-described method of driving an electro-optical device, it is preferable that the scanning electrode driving circuit for applying selection voltages to the scanning electrodes and the signal electrode driving circuit for applying signal voltages to the signal electrodes be integrated on a single-chip driving circuit IC. The integration of the scanning electrode driving circuit and the signal electrode driving circuit into the form of a single-chip integrated circuit results in a reduction in the total size of the device.
In the above-described method of driving an electro-optical device, of the scanning electrode driving circuit for applying selection-voltages to the scanning electrodes, the signal electrode driving circuit for applying signal voltages to the signal electrodes, and the power supply circuit for generating the selection voltages and the signal voltages, at least two circuits may preferably be integrated on a single-chip driving circuit IC. This allows a reduction in the number of integrated circuits used, and thus a reduction in the total size of the device.
In the above-described method of driving an electro-optical device, it is preferable that selection voltages used to select respective scanning electrodes be distributed and applied within one frame period. This allows an improvement in contrast and thus an improvement in quality of an image such as a still image displayed since selection periods are distributed within frame periods.
In the above-described method of driving an electro-optical device, it is also preferable that selection voltages used to select respective scanning electrodes be applied continuously during a predetermined period in one frame period. If this method is employed, when display data is read from a memory to create a signal voltage applied to the signal electrode in accordance with the display data, the display data becomes equal during the predetermined period. This means that the display data is held during the above-described predetermined period. This results in a reduction in the number of times that display data is read, and thus it becomes possible to reduce electric power consumed when display data is read.
In the above-described method of driving an electro-optical device, it is preferable that the plural number of scanning electrodes which are selected at the same time include a virtual scanning electrode, and the number of actual scanning electrodes which are equal to the plural number minus the number of virtual scanning electrodes are selected at the same time. For example, when the plural number of scanning electrodes which are selected at the same time is equal to eight, there may be for example one virtual scanning electrode. In this case, seven actual scanning electrodes are selected at the same time and thus the number of levels associated with the driving voltage can be reduced to five from the eleven which would otherwise be required.
In the above-described method of driving an electro-optical device, it is preferable that the plural number of scanning electrodes which are selected at the same time be equal to four. In this case, the number of levels associated with the driving voltage can be reduced to five. Alternatively, the plural number of scanning electrodes which are selected at the same time may preferably be equal to seven. In this case, the number of levels associated with the driving voltage can also be reduced to five.
In the above-described method of driving an electro-optical device, the scanning electrodes and the signal electrodes may preferably be arranged such that they intersect each other in a multiple-fold matrix. This allows a reduction in the number of scanning electrodes or the signal electrodes, and thus it becomes possible to simplify the circuit configuration of the driving circuits.
In the above-described method of driving an electro-optical device, it is preferable that a substrate on which the scanning electrodes are formed and a substrate on which the signal electrodes are formed be disposed such that they oppose each other, a single-chip driving circuit IC, including the scanning electrode driving circuit for applying selection voltages to the scanning electrodes and the signal electrode driving circuit for applying signal voltages to the signal electrodes in an integrated fashion, be mounted on one of the above-described two substrates, and the one of the two substrates be connected to the other substrate via an up-to-down conducting member. This allows a reduction in the size of the frame region of the electro-optical device.
According to another aspect of the present invention, an electro-optical device is provided including a plurality of scanning electrodes and a plurality of signal electrodes, the plurality of scanning electrodes and the plurality of signal electrodes being arranged such that they intersect each other, the plurality of scanning electrodes being organized into groups, each group consisting of a plural number of scanning electrodes which are simultaneously selected, selection of scanning electrodes being sequentially performed on a group-by-group basis, wherein: the electro-optical device includes a scanning electrode driving circuit for applying a scanning voltage to the scanning electrodes and also includes a signal electrode driving circuit for applying a signal voltage to the signal electrodes; and the amplitude of a voltage applied to the scanning electrodes is equal to the amplitude of a voltage applied to the signal electrodes.
This construction of the electro-optical device allows a reduction in the driving voltage and also a reduction in the number of levels associated with the driving voltage. As a result, it becomes possible to reduce the total electric power consumed by a power supply circuit which generates the driving voltage, driving circuits, a liquid crystal panel, and the like. Furthermore, the power supply circuit and the driving circuits can be constructed in simpler fashions. Still furthermore, the scanning electrode driving circuit is allowed to have a smaller breakdown voltage. This allows a reduction in cost. Still furthermore, it becomes possible to combine the power supply circuit, the control circuit, the signal electrode driving circuit, the scanning electrode driving circuit, and the like, in an integral fashion on a single chip, which results in a reduction in the total size.
In a preferable mode of the above-described electro-optical device, scanning voltages applied to the scanning electrodes include a non-selection voltage, a first selection voltage which is positive with respect to the non-selection voltage, and a second selection voltage which is negative with respect to the non-selection voltage, wherein maximum and minimum signal voltages applied to the signal electrodes are set to be equal to the first and second selection voltages described above. This makes it possible to use the maximum and minimum driving voltages in common for both the scanning electrode driving circuit and the signal electrode driving circuit, thereby reducing the number of levels associated with the driving voltages. Furthermore, because the amplitude of the voltage is equal for both driving circuits, the driving circuits are allowed to have an equal breakdown voltage, and thus, it becomes possible to integrate both driving circuits on a single chip.
In the above-described electro-optical device, the electro-optical device may be a liquid crystal display device, wherein it is preferable to employ a liquid crystal having a characteristic satisfying the condition: (root-means-square value of on-voltage applied to the liquid crystal)/(root-means-square value of off-voltage applied to the liquid crystal)xe2x89xa7(saturation voltage of the liquid crystal)/(threshold voltage of the liquid crystal), as a liquid crystal of the liquid crystal display device.
In the above-described electro-optical device, the power supply circuit for generating the scanning voltages and the signal voltages preferably includes a voltage boosting circuit for generating the first selection voltage by boosting the non-selection voltage and the second selection voltage, a first voltage dropping circuit for generating a signal voltage having a voltage level between the second selection voltage and the non-selection voltage, and a second voltage dropping circuit for generating a signal voltage having a voltage level between the non-selection voltage and the second selection voltage. This allows simplification in terms of the circuit configuration of the power supply circuit compared with the conventional power supply circuit. Furthermore, it becomes possible to integrate the power supply circuit together with the driving circuits on a single-chip integrated circuit.
In the above-described electro-optical device, of the scanning electrode driving circuit for applying selection voltages to the scanning electrodes, the signal electrode driving circuit for applying signal voltages to the signal electrodes, and the power supply circuit for generating the selection voltages and the signal voltages, at least two circuits may preferably be integrated on a single-chip driving circuit IC. This allows a reduction in the number of integrated circuits used, and thus a reduction in the total size of the device.
In the above-described electro-optical device, the scanning electrodes and the signal electrodes may be arranged such that they intersect each other in a multiple-fold matrix. This allows a reduction in the number of scanning electrodes or the signal electrodes, and thus it becomes possible to simplify the circuit configuration of the driving circuits.
In the above-described electro-optical device, it is preferable that a substrate on which the scanning electrodes are formed and a substrate on which the signal electrodes are formed be disposed such that they oppose each other, a single-chip driving circuit IC, including the scanning electrode driving circuit for applying selection voltages to the scanning electrodes and the signal electrode driving circuit for applying signal voltages to the signal electrodes in an integrated fashion, be mounted on one of the above-described two substrates, and the one of the two substrates be connected to the other substrate via an up-to-down conducting member. This allows a reduction in the size of the frame region of the electro-optical device.
According to still another aspect of the present invention, a driving circuit for driving an electro-optical device is provided including a plurality of scanning electrodes and a plurality of signal electrodes, the plurality of scanning electrodes and the plurality of signal electrodes being arranged such that they intersect each other, the plurality of scanning electrodes being organized into groups each consisting of a plural number of scanning electrodes which are simultaneously selected, selection of scanning electrodes being sequentially performed on a group-by-group basis, wherein the driving circuit includes a scanning electrode driving circuit for applying a scanning voltage to the scanning electrodes and also includes a signal electrode driving circuit for applying a signal voltage to the signal electrodes; the amplitude of the voltage applied to the scanning electrodes is equal to the amplitude of the voltage applied to the signal electrodes; and the scanning electrode driving circuit and the signal electrode driving circuit are integrated on a single-chip integrated circuit.
According to the present invention, this above described construction of the driving circuit allows a reduction in the driving voltage and also a reduction in the number of levels associated with the driving voltage. As a result, it becomes possible to reduce the total electric power consumed by a power supply circuit which generates the driving voltage, driving circuits, a liquid crystal panel, and the like. Furthermore, the power supply circuit and the driving circuits can be constructed in simpler fashions. Still furthermore, the scanning electrode driving circuit is allowed to have a smaller breakdown voltage. This allows a reduction in cost. Still furthermore, a reduction in the total size can be achieved as a result of the integration of the signal electrode driving circuit and the scanning electrode driving circuit on a single chip.
According to still another aspect of the present invention, there is provided an electro-optical device including: a pair of first and second substrates; a plurality of signal electrodes formed in an image display region on the first substrate, each signal electrodes including a plurality of pixel electrode sections; a plurality of scanning electrodes formed in the image display region on the second substrate, the plurality of scanning electrodes being arranged such that each of them intersects a plural number of adjacent pixel electrode sections located in a direction in which the plurality of signal electrodes are disposed; a driving circuit in the form of a single chip for driving the plurality of signal electrodes and the plurality of scanning electrodes, the driving circuit being connected to a predetermined point located on either the first or second substrate in a frame region surrounding the image display region; a plurality of first interconnection lines formed on either the first or second substrate in the frame region, the plurality of first interconnection lines connecting the driving circuit to one end of each of the plurality of signal electrodes; a plurality of up-to-down conducting elements disposed between the first and second substrates in the frame region, the plurality of up-to-down conducting elements being connected to the end portions of the respective plurality of scanning electrodes, the end portions being located in the frame region; and a plurality of second interconnection lines formed on either the first or second substrate in the frame region, the plurality of second interconnection lines connecting the driving circuit to the plurality of up-to-down conducting elements.
In this electro-optical device according to the present invention, a plurality of electrodes are formed in a multiple-fold matrix in the image display region, and the driving circuit in the single-chip form is mounted on a substrate at a predetermined location in the frame region and at the side of one end of the signal electrodes. In the frame region, one end, adjacent to the above-described predetermined location, of each of the plurality of signal electrodes is connected to the driving circuit via the corresponding first interconnection line. This makes it unnecessary to extend the first interconnection lines over long paths around the image display region. That is, the first interconnection lines are required to be formed only along short paths. When the electrodes are formed in an n-fold matrix (where n is an integer equal to or greater than 2), the width of each scanning electrodes is set to be equal to the total length of n pixels so that each scanning electrode means opposes an array of pixels formed with adjacent n signal electrodes. In this case, the total number of scanning electrodes becomes 1/n times the number of scanning electrodes which are required in the non-multiple matrix structure (that is, a single-fold matrix structure). The end of each of the reduced number of scanning, electrodes is connected, in the frame region, to the corresponding up-to-down conducting elements which is in turn connected to the driving circuit via the corresponding second interconnection line. Thus, the total number of second interconnection lines is reduced to a value as small as about 1/n times the number of second interconnection lines which are required in the non-multiple matrix structure. As a result, the area occupied in the frame region by the second interconnection lines can be reduced by a factor of about 1/n. That is, although the driving circuit is of the single-chip type, it is possible to effectively minimize the increase in the area occupied, in the frame region, by the second interconnection lines. On the other hand, because each scanning electrodes has a width n times the size of one pixel, high-precision microfabrication technology is not required. Thus, it becomes possible to combine the single-chip driving circuit with the signal electrodes in the multiple-fold matrix form.
According to the present invention, as described above, it is possible to reduce the frame region relative to the image display region by employing the first interconnection lines extending along rather short paths and a reduced number of second interconnection lines. Besides, the plurality of up-to-down conducting elements, which occupy a particular area in the frame region and which are required to be formed taking into account the alignment error which can occur when the first and second substrates are bonded to each other, are formed such that one up-to-down conducting elements is formed for each of the scanning electrodes, the total number of which is reduced by a factor of 1/n, where n is the degree of multiplicity. Therefore, the total number of up-to-down conducting elements can also be reduced by a factor of about 1/n, and thus, it becomes possible to further reduce the size of the frame region. Furthermore, the employment of the first interconnection lines extending along rather short paths and the reduced number of second interconnection lines makes it possible to minimize the total interconnection resistance from the driving circuit to the scanning electrodes or the signal electrodes. Thus, degradation of the image signal due to the increase in the interconnection resistance can be prevented. Furthermore, it also becomes possible to display a high-quality image using a driving circuit with a rather low driving capability or a driving circuit with a low breakdown voltage. The electric power consumed during the driving operation can also be reduced. Furthermore, the selection time period of the image signal during one frame can be increased by a factor of n, wherein n is the degree of multiplicity. Thus, the driving voltage may also be reduced by reducing the duty ratio. In this case, the actual effects is kept in which contrast ratio and luminance of the image displayed can also be enhanced.
According to the present invention, as described above, it is possible to reduce the size of the frame region relative to the image display region, and it is also possible to rather easily reduce the pixel pitch. It is also possible to display a high-quality image using a driving circuit with a rather low driving capability, or a driving circuit with a low breakdown voltage. This allows a reduction in the total power consumption of the device.
In the above-described electro-optical device, it is preferable that the plurality of scanning electrodes extend, in an interdigital fashion, from both sides of the image display region toward the inner area of the image display region. This allows a reduction in the number of up-to-down conducting members disposed at one side of the image display region to a value one-half the total number of scanning electrodes. Furthermore, it allows disposing of a half of second interconnection lines on the first substrate in an area of the frame region at one side of the image display region, and another half at the opposite side of the image display region. This allows the second interconnection lines to be equally distributed on both sides within the frame region surrounding the image display region. Thus, second interconnection lines, each having a particular width, and up-to-down conducting means, each having a particular area, can be disposed in an efficient fashion within the frame region which is limited in area.
In the above-described electro-optical device, it is preferable that the image display region be longer in a direction along the signal electrodes than in a direction along the scanning electrodes, and the signal electrodes and the scanning electrodes be formed such that the number of pixels formed in the image display region along the signal electrodes is greater than the number of pixels along the scanning electrodes. In this arrangement, the respective signal electrodes with the multiple-fold matrix structure extend in the longitudinal direction of the image display region, and thus the total number and the length of first interconnection lines, each connected to one end near the driving circuit of the corresponding signal electrodes, can be fixed regardless of the length of the image display region in the longitudinal direction thereof. As for the total number of scanning electrodes (that is the total number of second interconnection lines), it is required to increase only one scanning electrodes (that is, one second interconnection line) each time the number of pixels in the longitudinal direction is increased by n. In this case, it is required to increase the length of the second interconnection lines only by an amount corresponding to the increase in the length of the image display region in the longitudinal direction. Thus, the present invention provides greater advantages in particular when the length of the image display region in the longitudinal direction becomes longer.
In the above-described electro-optical device, it is preferable that each up-to-down conducting elements includes an up-to-down conducting member disposed between the first and second substrates, and an up-to-down conducting terminal formed on either one of the first and second substrates, the up-to-down conducting terminal being in contact with the up-to-down conducting member and being connected to one end of a corresponding second interconnection line. In this arrangement, scanning electrodes are connected to the corresponding up-to-down conducting members disposed between the first and second substrates, wherein the up-to-down conducting members are connected to the corresponding up-to-down conducting terminals, which are in turn connected to the respective ends of the corresponding second interconnection lines formed on the first substrate, so that the driving circuit can supply a driving voltage to the scanning electrodes via the second interconnection lines, the up-to-down conducting terminals, and the up-to-down conducting members, thereby driving the scanning electrodes. Furthermore, it is possible to reduce the total number of up-to-down connecting terminals which occupy a particular area in the frame region, and which are required to be formed taking into account the alignment error which can occur when the first and second substrates are bonded to each other, by a factor of 1/n. This makes it very easy to reduce the size of the frame region in which the up-to-down connecting terminals are disposed.
In the above-described electro-optical device, it is preferable that each of the plurality of signal electrodes includes pixel electrodes, a signal interconnection line connected to the pixel electrodes, and two-terminal non-linear elements connected between the respective pixel electrodes and the signal electrode. This makes it possible to drive the respective pixel electrodes by means of switching via two-terminal non-linear elements such as TFDs (Thin Film Diodes), thereby displaying a high-quality image with high contrast, which makes the active matrix driving possible.
In the above-described electro-optical device, it is preferable that the driving circuit is mounted on the first substrate. This makes it possible to realize a small-sized light-weight low-power electro-optical device including a driving circuit mounted on a first substrate by means of the COG (Chip On Glass) technique.
In the above-described electro-optical device, it is preferable that input terminals be formed at the predetermined location on either the first or second substrate such that the input terminals are connected to the first and second interconnection lines, and that the driving circuit be connected to the input terminals via particular connection means. In this electro-optical device, because the driving circuit is connected to the first substrate via particular connection means such as a TAB (Tape Automated Bonding) film, a dedicated connector, or an ACF (Anisotropic Conductive Film), it becomes possible to design the electro-optical device in various fashions as required, and a reduction in cost can be achieved.
In the above-described electro-optical device, the signal electrodes and the scanning electrodes may be replaced with each other. In this case, the scanning electrodes are formed in a multiple-fold matrix on the first substrate on which the driving circuit is mounted, and thus it is possible to reduce the number of up-to-down conducting elements connected to the signal electrodes formed on the second substrate, and it is also possible to reduce the number of second interconnection lines. This allows the pixel pitch to be relatively easily reduced while reducing the size of the frame region relative to the image display region. Furthermore, it also becomes possible to display a high-quality image using a driving circuit having a low breakdown voltage and low voltage supply capability. A reduction in the total power consumption is also achieved. Furthermore, it is possible to display a high-quality image using a driving circuit having low capability of driving the signal electrodes (that is, capability of supplying the image signal voltage).
The present invention also provides an electronic apparatus using any electro-optical device described above as a display device. This makes it possible to realize an electronic apparatus including a display device with a small frame region.